1. Field of the Invention
This invention relates to a shift control system for a working vehicle having a propelling stepless transmission. More particularly, the invention relates to a shift control system having a shift pedal, a first linkage mechanism for transmitting a downward displacement of the shift pedal to the stepless transmission to change a shift position of the stepless transmission, a retaining mechanism for producing a retaining position corresponding to the shift position to retain the shift position of the stepless transmission, and a shift lever for setting the retaining position to be retained by the retaining mechanism.
2. Description of the Related Art
An agricultural tractor which is one example of working vehicles may include a hydrostatic stepless transmission for propelling the tractor. A shift pedal and the stepless transmission are interlocked through a linkage mechanism (e.g. a mechanical linkage mechanism with a linkage rod and the like for interlocking the shift pedal and stepless transmission, or an electric or hydraulic linkage mechanism for shifting the stepless transmission with an electric motor or hydraulic actuator in response to a control position of the shift pedal). The stepless transmission is shifted through the linkage mechanism in response to a depression of the shift pedal.
When the agricultural tractor engages in a grass cutting operation with a mower unit attached thereto, the grass cutting operation is carried out in many cases while running at a fixed speed. Thus, the agricultural tractor may include a retaining mechanism for retaining the stepless transmission in a desired shift position, and a shift lever for operating the retaining mechanism. The tractor can run at a fixed speed by operating the retaining mechanism with the shift lever to retain the stepless transmission in the desired shift position, without depressing the shift pedal. This is usually called a cruising function.
Two types of models may be manufactured as working vehicles such as agricultural tractors having a propelling stepless transmission, one with the above retaining mechanism and the other without it. The type with the retaining mechanism must have a construction for mechanically interlocking the retaining mechanism and stepless transmission so that the retaining mechanism is operable to retain the stepless transmission in a desired shift position.
Consequently, when manufacturing the type with the retaining mechanism, the construction of the type without the retaining mechanism (e.g. the linkage mechanism interlocking the shift pedal and stepless transmission) may be altered to mechanically interlock the retaining mechanism and stepless transmission) Then, productivity may be lowered in manufacturing the type with the retaining mechanism and the type without it.
An object of this invention is to provide a shift control system for a working vehicle having a propelling stepless transmission, which improves productivity in manufacturing the type of vehicle with a retaining mechanism for retaining the stepless transmission in a desired shift position, and the type having no such retaining mechanism.
To fulfilled the above object, this invention proposes a shift control system as set forth at the outset hereof, wherein a second linkage mechanism is provided for transmitting of an operating displacement of the shift lever to the shift pedal to displace the shift pedal to a depressed position corresponding to the retaining position set by the shift lever and retained by the retaining mechanism.
In a working vehicle having a propelling stepless transmission, for example, the shift pedal and stepless transmission may be interlocked through a first linkage mechanism. The stepless transmission is shiftable by a depression of the shift pedal through the first linkage mechanism. When adding a cruising function to such a working vehicle with a retaining mechanism provided for retaining in a desired shift position, and a shift provided for operating the retaining mechanism, the retaining mechanism and shift lever are mounted on a vehicle body, and the retaining mechanism and the shift pedal are interlocked through the second linkage mechanism. With this construction, by operating the shift lever, the shift pedal may be operated to and retained in a desired shift position through the retaining mechanism and second linkage mechanism. Through the shift pedal and first linkage mechanism, the stepless transmission may be retained in a desired shift position.
That is, when providing the retaining mechanism and shift lever for the vehicle body of the type of vehicle not having the retaining mechanism, it is necessary only to interlock the retaining mechanism and shift pedal through the second linkage mechanism. The type of vehicle having the retaining mechanism (i.e. the cruising function) may be obtained with little or no modification made to the first linkage mechanism interlocking the shift pedal and stepless transmission.
When manufacturing the type of vehicle with the retaining mechanism and the type of vehicle without it, the latter may be manufactured without modification, whereas the type with the retaining mechanism may be obtained by adding the retaining mechanism and shift lever to the vehicle body of the type not having the retaining mechanism, and interlocking the retaining mechanism and shift pedal through the second linkage mechanism.
In a preferred embodiment of this invention, the shift lever, retaining mechanism and second linkage mechanism are attachable and detachable independently of the first linkage mechanism. This construction realizes, in a simple way, the cruising type by incorporating the retaining mechanism as an option, and the non-cruising type by removing the retaining mechanism, which may be done at any time as desired.
In a preferred embodiment of this invention, the second linkage mechanism includes a play-accommodating mechanism for permitting a depression of the shift pedal to a higher speed position than the retaining position retained by the retaining mechanism, the play-accommodating mechanism permitting the shift pedal to be depressed the retaining position retained by the retaining mechanism to the higher speed position. With this construction, when the driver desires to temporarily accelerate the type of vehicle having the retaining mechanism and running with the shift pedal, and thus the stepless transmission, retained in a selected shift position by the retaining mechanism, the driver may cause the vehicle to run temporarily at high speed by depressing the shift pedal from the selected shift position to a higher speed position.
In another preferred embodiment of this invention, the retaining mechanism, shift lever and second linkage mechanism are mounted on a support member. The retaining mechanism, shift lever and second linkage mechanism by means of the support member constitute a single unit. To obtain the type of vehicle with the retaining mechanism, the support member may be attached to the vehicle body to incorporate the retaining mechanism, shift lever and second linkage mechanism into the vehicle body. There is no need to attach the retaining mechanism shift lever and second linkage mechanism individually to the vehicle body.
In a working vehicle having the stepless transmission is disposed between right and left body frames, and the shift pedal disposed laterally outwardly of the right body frame, and the first linkage mechanism extending through the right body frame for interlocking the shift pedal and stepless transmission, this invention proposes to interlock the retaining mechanism and shift pedal through the second linkage mechanism laterally outwardly of the right body frame. With this construction, when the retaining mechanism and shift lever are added to a vehicle body of the type having no retaining mechanism, the retaining mechanism and shift pedal may be interlocked easily through the second linkage mechanism laterally outwardly of the right body frame. The type of vehicle having the retaining mechanism may be obtained with little or no modification made to the first linkage mechanism interlocking the shift pedal and stepless transmission.
In a working vehicle such as an agricultural tractor, the stepless transmission is steplessly shiftable forward and backward, and the shift pedal may include a forward pedal portion extending forward, and a rearward pedal portion extending rearward, the forward pedal portion being depressible to shift the stepless transmission for high forward speed, the rearward pedal portion being depressible to shift the stepless transmission for high backward speed. For such a working vehicle, this invention proposes to dispose the retaining mechanism rearwardly of the shift pedal, and to interlock the retaining mechanism and the rearward pedal portion through the second linkage mechanism. Since the retaining mechanism is disposed close to the shift pedal according to this construction, the retaining mechanism and shift pedal may be interlocked easily through the second linkage mechanism. The second linkage mechanism may be reduced in length.
Other features and advantages of this invention will be apparent from the following description of the embodiments to be taken with reference to the drawings.